1. Field of the Invention
The present invention relates generally to a wheel velocity detecting apparatus and, more particularly, to an apparatus which has improved accuracy in detecting a wheel velocity chiefly in a low velocity range by processing a signal from a rotary sensor (pickup sensor).
2. Description of the Related Art
Conventionally there is known a wheel velocity detecting apparatus for detecting a signal from an electromotive force or a frequency corresponding to the rotational speed of wheels by a pickup coil arranged near a wheel and converting the signal into a square wave to detect a wheel velocity based on an edge interval of the square wave.
For example, Japanese Patent Laid-Open Publication No. Hei 3-18756 discloses a technique for detecting a wheel velocity by generating a square wave of duty ratio 1:1 from a sensor signal to detect a wheel velocity based on an edge interval of the square wave pulse and the circumference of the wheel.
However, when a wheel velocity is detected by generating a square wave pulse from a sensor signal at a very low velocity (for example, 10 km/h or lower), an edge is not inputted in time, even at the updating timing of the wheel velocity, so that the wheel velocity has to be derived from an estimation, which causes a problem of prohibiting accurate detection of the wheel velocity.
It is naturally conceivable that a wheel velocity may be uniformly set at 0 km/h during a very low velocity, but this does not solve the problem, as a wheel velocity still fails to be accurately detected.